1. Field of the Invention
The present invention relates to an optical recording medium for recording a signal both on a groove and land, and a production method of the same.
2. Description of the Prior Art
For a rewritable high-density optical recording medium, especially a magneto-optical recording medium, a format to realize a capacity as large as 5 to 7 GB on one side (a diameter of 12 cm, i.e., a so called CD size) has been suggested by providing a disc substrate having a thickness of only 0.6 mm, with a numerical aperture NA of 0.6 in an optical system, a single-plate configuration for enabling magnetic field modulation, a recording/reproduction laser wavelength of 630 to 60 nm, a track pitch of 0.6 .mu.m, a recording density of 0.20 .mu.m/bit.
In this case, the groove configuration is a land/groove recording method which is advantageous for a high density.
In the aforementioned land/groove recording method, both of the land and groove are formatted so as to be capable of recording and reproduction and the optical disc has two-spiral configuration of the land and groove.
The land/groove format is an advantageous format for reducing the track pitch. When a tracking signal is fetched with a push-pull signal, it is possible to obtain a signal from two tracks. Accordingly, it is possible to create an error signal up to a half of a conventional track pitch and its polarity is used to identify a land and a track.
Moreover, in reproduction from a magneto-optical recording medium, it is possible to carry out an optical mask based on a difference in the depth of the land and groove. By effectively selecting a depth, it is possible to reduce a cross talk from an adjacent track.
In the aforementioned land/groove recording method also, it is necessary to provide a control signal such as a clock signal for detecting a head of an information signal, and a format for a fine clock has been studied.
In this case, a clock mark is a head detecting signal and should not require a large area.
To cope with this, there has been suggested a technique to provide an address signal and a clock signal by wobbling a groove and to increase efficiency by sharing the clock signal with a data block.
However, this technique has a problem that a jitter is generated in a clock extraction if a recording spot is deviated from the track center.